Wi-Fi was first deployed in an unlicensed frequency band which was used for Industrial, Scientific and Medical (ISM) equipment. The ISM frequency band spans from 2.4 to 2.5 GHz and is referred to as the 2.4 GHz band. There are 14 channels defined for use by Wi-Fi IEEE 802.11 for the 2.4 GHz ISM band. Not all of the channels are allowed in all countries: 11 are allowed by the FCC (Federal Communication Commission) and used in what is often termed the North American domain, and 13 are allowed in Europe where channels have been defined by ETSI (European Telecommunications Standards Institute). The WLAN/Wi-Fi channels are spaced 5 MHz apart (with the exception of a 12 MHz spacing between the last two channels).
The IEEE 802.11 WLAN standards specify a bandwidth of 22 MHz and channels are on a 5 MHz incremental step. Nominal figures for the channel bandwidth of 20 MHz are often given. The 20/22 MHz bandwidth and channel separation of 5 MHz means that adjacent channels overlap and signals on adjacent channels will interfere with each other.
As the 2.4 GHz band becomes more crowded, many users are opting to use the 5 GHz ISM band. This not only provides additional spectrum, but it is not as widely used by appliances including items such as microwave ovens, etc.
The 5 GHz Wi-Fi bandwidth includes unlicensed ISM channels as well as numerous channels that fall outside the accepted ISM unlicensed band and, as a result, various restrictions are placed on operation at these frequencies. The main concern for using channels that fall outside the ISM unlicensed band is that the Wi-Fi equipment may interfere with operations of weather-radar and military applications (such as military radar and/or communications). To prevent interference, Wi-Fi equipment that operates in these frequencies must implement Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) capabilities on these channels.
DFS is a spectrum-sharing mechanism that allows wireless LANs (WLANs) to coexist with radar and other systems. A DFS system listens on a specific band for signal from, e.g., a radar system. If the DFS system detects a signal, the DFS system automatically selects a different frequency and examines the different frequency to see if there is any other equipment operating on it. The DFS system then selects and uses a 5 GHz frequency channel that does not interfere with any radar system.
DFS rules only apply to the frequency band between 5.250 and 5.725 GHz, which is the frequency band used by weather and military radars. It should be noted that DFS based systems are effective only when the incumbent system includes a transmitter that operates over the same frequency channel and as such announces the existence of a receiver on that frequency channel.
TPS is an automatic protocol by which two devices initiating communication in the 5 GHz spectrum will negotiate so that their respective power level is as low as possible, just high enough to hear each other. This arrangement reduces signal pollution and thus reduces interference with other devices. It should be noted that systems that utilize TPS may initially interfere with other systems, and may mitigate this interference only after the two communicating endpoints negotiate and reduce the transmission power.
U.S. patent application Ser. No. 15/379,131, entitled “Computing Protection Zones For Avoidance Of Interference In Wireless Communications,” which is incorporated herein by reference in its entirety, describes a method for calculating (by a channel master) protection zones and causing the terminal to determine whether to perform or prevent an attempted transmission to an intended receiver.
U.S. patent application Ser. No. 15/455,687, entitled “Server Participation In Avoidance Of Interference In Wireless Communications,” which is incorporated herein by reference in its entirety, assumes that an initial communication between a mobile terminal and a satellite has been established. The patent applicant describes methods by which the channel master (based on information it has and the client does not have) can instruct the client to change its transmission parameters in order to optimize the network.
U.S. patent application Ser. No. 15/455,775, entitled “Reduced Power For Avoidance Of Interference In Wireless Communications,” which is incorporated herein by reference in its entirety, assumes that the terminal and the satellite were able to establish a non-interfering communication channel. Over this communication channel, the channel master should be able to broaden the communication choices (satellites and channels) that the terminal can use, effectively reducing the size of the protection zones that govern the operations of that terminal.
In all of these patent disclosures, the ground station communicates with terminals via a satellite using a directional antenna pointing towards the satellite. The channel used by the ground station for the forward path and the channels used by the satellite to transmit both on the forward and backward channels are licensed from and registered with the FCC. This ensures that none of these transmissions interfere with Point-to-Point Receivers (PtPRs).